1. Field of the Invention
This invention relates to a novel loudspeaker employing a compound material of a polyamide resin and glass particles for a diaphragm, and a method for the preparation thereof.
2. Description of Related Art
Recently, as the acoustic equipment, such as audio amplifier, is improved in performance, large level signals (large input) are liable to be applied to the loudspeaker, so that a demand is raised for improving its input resistance.
If a large input is applied to a loudspeaker, there is evolved heat in a voice coil section driving the diaphragm, thus thermally damaging the diaphragm. For example, polypropylene, so far used perferentially as a diaphragm material, has a thermal deformation temperature as low as approximately 100xc2x0 C. (ASTM D648:0.455 MPa), and hence a problem is raised that the diaphragm made of polypropylene is deformed by the large input, thus possibly destructing the loudspeaker.
By way of a countermeasure therefor, there is proposed a diaphragm for a loudspeaker employing a polyimide based resin, as a highly heat-resistant material, a liquid crystal polymer, or a heat-resistant resin, such as polyetherketone resin.
However, the high thermal resistance indicates forming difficulties, thus possibly leading to the lowering of productivity and to the increased manufacturing cost. Moreover, the material itself is expensive, thus leading to increased overall cost.
For resolving the above problem, such a diaphragm is proposed which employs a polyamide resin having a higher thermal deformation temperature of approximately 190xc2x0 C., or a compound material formed of the polyamide resin admixed with inorganic fillers, such as glass fibers, carbon fibers, mica powders or calcium carbonate.
In these materials, the heat-related problems are resolved. However, there is presented such a problem that, due to significant changes in the modulus of elasticity caused by hygroscopicity proper to the amide resin, the playback frequency response of the loudspeaker employing these materials for the diaphragm is changed significantly between that in the dry state and that in the humid state.
It is therefore an object of the present invention to provide a loudspeaker having superior input resistance properties and superior moisture-proofness and which is not prone to destruction even under a large input such that the replay frequency response is not affected by humidity.
The present inventors have conducted eager researches, and found that the above object can be accomplished by using a homogeneous composite consisting of microscopic glass particles and a polyamide type resin, obtained by polyamide synthesis in the presence of water glass, as an acoustic diaphragm. This finding has led to completion of the present invention.
In one aspect, the present invention provides a diaphragm for a loudspeaker including a compound material containing glass particles having a particle size of 8 to 300 nm and a polyamide resin, in which the compound material is a sheet-like member formed by a paper-making technique.
In another aspect, the present invention provides a method for the preparation of a diaphragm for a loudspeaker including contacting a phase of an aqueous solution containing a diamine and water glass and a phase of an organic solution containing a dicarboxylic acid halide to generate a compound material containing glass particles and a polyamide resin, and forming the resulting compound material to the shape of a diaphragm by application of a paper-making technique.
The polyamide resin has a higher thermal deformation temperature and satisfactory castability. However, if used alone, the polyamide resin undergoes marked change in the modulus of elasticity due to its hygroscopicity.
On the other. hand, with a glass/polyamide compound material, in which extremely fine glass particles are homogeneously dispersed in the polyamide, these changes in the modulus of elasticity caused by moisture absorption may be eliminated to assure high thermal resistance and only slight lowering of the physical properties ascribable to moisture absorption.
Therefore, in a speaker employing this compound material as a diaphragm, the input resistance is improved, while the reproducing frequency response is not affected by humidity.
Moreover, in the compound material obtained on contacting the aqueous solution containing the diamine and water glass and the organic solution containing the dicarboxylic acid halide, the glass particles are homogeneously dispersed in the fibrous polyamide resin, such that it can be readily formed to the shape of a diaphragm by the customary paper-making method.
That is, according to the present invention, employing a sheet-like material, mainly composed of a compound material composed of extremely fine glass particles are homogeneously dispersed in the polyamide, as a diaphragm, the input resistance and the moisture-proofness can be improved appreciably.